Liquid crystal compounds, mixtures and devices

ABSTRACT

Liquid crystal compounds having the formula (I) ##STR1## in which A 1  is alkyl, alkoxy or alkenyl; X 1 , X 2 , X 3  and X 4  are independently halogens, m, n, p and q are independently 0, 1, 2, 3 or 4 such that m+n+p+q≠0; Y is O or COO; and A 2  is an end group of the formula (II), ##STR2## where Z is halogen, CH 3 , CN, CF 3  or, CHF 2  ; R is a linear or branched alkyl group or H; and R 1  is a linear or branched alkyl group or H.

This application is a 371 of PCT/GB93/01133 filed May 23, 1993.

This invention relates to novel liquid crystal compounds, liquid crystalmaterials containing them and their inclusion in liquid crystal devices.

Liquid crystals can exist in various phases. In essence there are threedifferent classes of liquid crystalline material, each possessing acharacteristic molecular arrangement. These classes are nematic,cholesteric and smectic. A wide range of smectic phases exists, forexample smectic A and smectic C. Some liquid crystal materials possess anumber of liquid crystal phases on varying the temperature, others havejust one phase. For example, a liquid crystal material may show thefollowing phases on being cooled from the isotropicphase:--isotropic--nematic--smectic A--smectic C--solid. If a materialis described as being smectic A then it means that the materialpossesses a smectic A phase over a useful working temperature range.

Compounds such as: ##STR3## are described in J. Am. Chem. Soc., 1989,111, 8119-8125 by J. W. Goodby et. al., where n ranges from 8 to 16. Atlong n-alkoxy chain lengths the series exhibits a novel variation ofmesophase behaviour to which a smectic A* phase was assigned. Some ofthe materials also appeared to exhibit two further mesophases.

According to this invention there are provided compounds having ageneral formula I ##STR4## in which A₁ is selected from alkyl, alkoxy oralkenyl; X₁, X₂, X₃ and X₄ are independently selected from the halogengroup; m, n, p and q are independently 0, 1, 2, 3 or 4 such thatm+n+p+q≠0; Y is selected from O and COOO; A₂ is an end group of formulaII ##STR5## where Z is selected from halogen, CH₃, CN, CF₃, CHF₂ ; R isa linear or branched alkyl group or H; R₁ is a linear or branched alkylgroup or H.

Preferably A₁ is C₃₋₂₀, more preferably C₆₋₁₆, even more preferablyC₉₋₁₅.

Preferably A₂ is a chiral end group.

Preferably R is C₂₋₁₅, more preferably C₃₋₁₀, even more preferably C₅₋₇.

Preferably R₁ is C₁₋₅, more preferably H.

Preferably Z is CH₃ or CN.

Preferably X is F.

Preferably each of m n, p and/or q is independently 1 or 2 such thatm+n+p+q=1 or 2.

Compounds of Formula I can be included in a material, the material beinga mixture of compounds.

The materials of this aspect of the invention may be used in many of theknown forms of liquid crystal display devices, for example chiralsmectic electrooptic devices. Such a device may comprise a layer ofliquid structures and surface treated to align liquid crystal materialmolecules. The liquid crystal mixtures may have applications inferroelectric, ferrielectric (M. Johno et al., Japan Display, 1989, 22),antiferroelectric, thermochromic and electroclinic devices; they mayalso lead to the formation of frustrated liquid crystal phases.Frustrated phases arise from mesophases possessing double twiststructures which means that space cannot be filled uniformly and thephase is stabilised via a lattice of defects. Frustrated phases can alsoarise from the competition between helical and layer structures, anexample of which is the smectic A* analogue of the Abrikson flux phaseas described by J. W. Goodby, M. A. Waugh, S. M. Stein, E. Chin, R.Pindak, Nature, 1989, 337, 449; A. J. Slaney and J. W. Goodby, J. Mater.Chem. 1991, 1, 5. The competition between helical and layer structuresleads to defects being formed which again stabilise the phase.

Ferroelectric smectic liquid crystal materials, which can be produced bymixing an achiral host and a chiral dopant, use the ferroelectricproperties of the tilted chiral smectic C, F, G, H, I, J and K phases.The chiral smectic C phase is denoted S_(c) * with the asterisk denotingchirality. The S_(c) phase is generally considered to be the most usefulas it is the least viscous. Ferroelectric smectic liquid crystalmaterials should ideally posses the following characteristics: lowviscosity, controllable spontaneous polarisation (Ps) and an S_(c) phasethat persists over a broad temperature range, which should includeambient temperature and exhibits chemical and photochemical stability.Materials which possess these characteristics offer the prospect of veryfast switching liquid crystal containing devices. Some applications offerroelectric liquid crystals are described by J. S. Patel and J. W.Goodby in Opt. Eng., 1987, 26, 273.

The electroclinic effect, first described by S. Garoff and R. Meyer,Phys. Rev. Lett., 38, 848, 1977, usually occurs in the smectic A phase.Unlike ferroelectric devices, the liquid crystal material inelectroclinic devices is not bistable. The liquid crystal directorwithin an EC device responds almost linearly to an applied electricfield. Electroclinic devices are suitable for various applicationsincluding spatial light modulators.

Chadani et al., Jpn. J. Appl. Phys., 27, L 729, 1988; Jpn. J. Appl.Phys., 28, L 1261, 1989; Jpn. J. Appl. Phys., 28, L 1265, 1989, firstdescribed and antiferroelectric effect which is a tri-stable switchingstate occurring in a liquid crystal phase designated as SmC_(A) *. Forexample, when ferroelectric layers are stacked so that an thepolarisation vectors in sequential layers oppose one another then anantiferrelectric phase is obtained.

For a review of thermochromism in liquid crystals see J. G. Grabmaier in`Applications of Liquid Crystals`, G. Meier, E. Sackmann and J. G.Grabmaier, Springer-Verlag, Berlin and New York, 1975, pp 83-158.

For all the above applications it is not usual for a single compound toexhibit all of the properties highlighted, for example ferroelectricsmectic liquid crystal materials generally consist of a mixture ofcompounds which when mixed together induce a chiral tilted smectic phasechiral dopants are added to a liquid crystalline mixture in order toinduce the smectic mixture to become chiral smectic and to induce a Psin the material, or if the material already possesses a Ps then theintroduction of a chiral dopant should result in a change of value forPs.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example only withreference to the accompanying drawings of which:

FIG. 1 describes a synthetic route for the preparation of examplecompounds 46 to 65, i.e. compounds of general formula VII where X and Yare described in Tables 5 and 6.

FIG. 2 illustrates a liquid crystal device.

FIGS. 3-12 are phase diagrams for compounds 46-65 (R) and (S) mixtures.

FIGS. 13 and 14 are graphs of optical tilt angle/° versus reducedtemperature/°C. for compounds 52 and 56 respectively.

DETAILED DESCRIPTION OF THE INVENTION ##STR6##

Reagents used in the synthetic route of FIG. 1 are shown in Route 1.

Compound 1 is synthesized from 3-fluorophenol (Fluorochem Ltd) by a fastbromination at -5° C. (Br₂, acetic acid). Compound 2 is commerciallyavailable from Fluorochem Ltd. Compound 39 is a commercially availableliquid crystal precursor from Merck. ##STR7##

Route 1

The steps are identified below:

1a RBr, K₂ CO₃, butanone, reflux.

1b 3-methylbut-1-yn-3-ol, Pd(PPh₃)₄, CuI, (^(i) Pr)₂ NH, N₂, reflux.

1c KOH, toluene, N₂, reflux.

1d (i) BuLi, THF, N₂, -10° C; (ii) CO₂ (s), THF, -10° C. to RT; (iii)HCl (conc).

2a H₂ SO₄, AcOH, H₂ O, reflux.

2b (i) NaOH, CH₃ OCOCl, H₂ O, 0° C.; (ii) 1:1 Hcl:H₂ O, pH=5.

2c (R)- or (S)-2-octanol, diethyl azodicarboxylate, PPh₃, THF, N₂, RT.

2d EtOH, NH₃ (aq), RT.

2e Dicyclohexylcarbodiimide, 4-N,N-dimethylaminopyridine, CH₂ Cl₂, RT.

This route allows the configuration about the chiral carbon to be easilycontrolled.

COMPOUND 3 Preparation of 1-Bromo-4-dodecyloxy-2-fluorobenzene

1-Bromodecane (12.01 g, 48.2 mmol) in butanone (20 ml) was addeddropwise to a stirred, refluxing mixture of 4-bromo-3-fluorophenol (1)(9.04 g, 47.4 mmol), potassium carbonate (10.12 g, 73.2 mmol) andbutanone (100 ml). The resulting reaction mixture was refluxed for afurther 20 hours. The cooled reaction mixture was then filtered toremove the excess potassium carbonate and precipitated potassiumbromide. The filtrate was washed with 5% (v/v) sodium hydroxide (2×50ml) then water (50 ml) and the organic layer then dried (MgSO₄),filtered and evaporated under reduced pressure to give a colourless oilwhich was purified by column chromatography [silica gel: 1:1dichloromethane-petrol (bp 40°-60° C.)] to give a colourless liquid.This was then dried in vacuo (P₂ O₅, 0.20 mm Hg, RT, 5 h).

Yield=16.73 g, (98%)

Compounds 3-11 have general formula III, see Table 1. ##STR8##

COMPOUND 4 Preparation of 1-Bromo-2-fluoro-4-tridecyloxybenzene

This was prepared using a similar method to that described for compound3. Quantities: compound 1 (4.02 g, 21.1 mmol), 1-bromotridecane (6.11 g,23.2 mmol), potassium carbonate (5.22 g, 37.8 mmol) and butanone (115ml).

Yield=6.62 g, (84%) mp=26°=27° C.

COMPOUND 5 Preparation of 1-Bromo-2-fluoro-4-tetradecyloxybenzene

This was prepared using a similar method to that described for compound3. Quantities: compound 1 (4.03 g, 21.1 mmol), 1-bromotetradecane (6.41g, 23.1 mmol), potassium carbonate (5.59 g, 40.5 mmol) and butanone (115ml).

Yield=7.48 g, 92%) mp=30°-31° C.

COMPOUND 6 Preparation of 1-Bromo-2-fluoro-4-pentadecyloxybenzene

This was prepared using a similar method to that described for compound3. Quantities: compound 1 (2.31 g, 12.1 mmol), 1-bromopentadecane (3.97g, 13.6 mmol), potassium carbonate (2.97 g, 21.5 mmol) and butanone (80ml).

Yield=4.35 g, (90%) mp=32°-36° C.

COMPOUND 7 Preparation of 1-Bromo-4-dodecyloxy-3-fluorobenzene

This was prepared using a similar method to that described for compound3. Quantities: compound 2 (6.00 g, 31.4 mmol), 1-bromododecane (8.23 g,33.1 mmol), potassium carbonate (5.67 g, 40.9 mmol) and butanone (100ml).

Yield=11.11 g, (99%)

COMPOUND 8 Preparation of 1-Bromo-3-fluoro-4-tridecyloxybenzene

This was prepared using a similar method to that described for compound3. Quantities: compound 2 (6.01 g, 31.5 mmol), 1-bromotridecane (8.75 g,33.2 mmol), potassium carbonate (5.67 g, 40.9 mmol) and butanone (100ml).

Yield=11.69 g, (99%) mp=37°-39° C.

COMPOUND 9 Preparation of 1-Bromo-3-fluoro-4-tetradecyloxybenzene

This was prepared using a similar method to that described for compound3. Quantities: compound 2 (6.02 g, 31.5 mmol), 1-bromotetradecane (9.15g, 33.0 mmol), potassium carbonate (5.67 g, 40.9 mmol) and butanone (100ml).

Yield=11.82 g, (97%) mp=28°-29° C.

COMPOUND 10 Preparation of 1-Bromo-3-fluoro-4-pentadecyloxybenzene

This was prepared using a similar method to that described for compound3. Quantities: compound 2 (5.04 g, 26.4 mmol), 1-bromotetradecane (8.15g, 27.9 mmol), potassium carbonate (5.65 g, 40.9 mmol) and butanone (120ml).

Yield=9.54 g, (90%) mp=40°-43° C.

COMPOUND 11 Preparation of 1-Bromo-3-fluoro-4-hexadecyloxybenzene

This was prepared using a similar method to that described for compound3. Quantities: compound 2 (5.02 g, 26.3 mmol), 1-bromohexadecane (8.56g, 28.0 mmol), potassium carbonate (5.19 g, 37.6 mmol) and butanone (100ml).

Yield=10.09 g, (92%) mp=41°-43° C.

COMPOUND 12 Preparation of4-Dodecyloxy-2-fluoro-1-(3-hydroxy-3-methylbut-1-ynyl)benzene

A stream of dry nitrogen was bubbled through a stirred, dark greenmixture of compound 3 (5.00 g, 12.9 mmol), palladium (O)tetrakis(triphenylphosphine) (1.02 g, 0.89 mmol), copper (I) iodide(0.11 g, 0.58 mmol) and dry di-isopropylamine (30 ml) for a period of 10min. A solution of 3-methylbut-1-yn-3-ol (2.54 g, 30.2 mmol) in drydi-isopropylamine (10 ml) was added dropwise at room temperature; thereaction mixture turned deep orange-brown. The reaction was then heatedfor 4 hours under gentle reflux under nitrogen. The cooled reaction wasfiltered through a pad of `Hyflo-supercel` and water (50 ml) added tothe filtrate. The crude product was then extracted using diethyl ether(3×50 ml); the combined ethereal extracts were then washed with brine(50 ml), dried (MgSO₄), filtered and evaporated to give a brown oil.This was then purified by flash chromatography [fine mesh silica gel;9:1 dichloromethane-petrol (bp 40°-60° C.)] to give a brown solid whichwas recrystallised from cyclohexane and dried in vacuo (P₂ O₅, 0.30 mmHg, RT, 4 hours).

Yield=4.70 g, (93%) mp=43°-46° C.

Compound 12-20 have general formula IV, see Table 2. ##STR9##

COMPOUND 13 Preparation of2-Fluoro-1-(3-hydroxy-3-methylbut-1-ynyl)-4-tridecyloxybenzene

This compound was prepared using a similar method to that described forcompound 12. Quantities: compound 4 (5.18 g, 13.9 mmol), palladium (O)tetrakis(triphenylphosphine) (1.03 g, 0.91 mmol), copper (I) iodide(0.68 mmol), 3-methybut-1-yn-3-ol (2.54 g, 30.2 mmol) anddi-isopropylamine (50 ml). The crude product was purified by flashchromatography [fine mesh silica gel; 10% (v/v) ethyl acetate in petrol(bp 40°-60° C.)] to give a yellow solid which was recrystallized fromcyclohexane and dried in vacuo (P₂ O₅, 0.20 mm Hg, RT, 18 hours).

Yield=3.17 g, (58%) mp=35°-36° C.

COMPOUND 14 Preparation of2-Fluoro-1-(3-hydroxy-3-methylbut-1-ynyl)-4-tetradecyloxybenzene

This compound was prepared using a similar method to that described forcompound 12. Quantities: compound 4 (5.40 g, 13.95 mmol), palladium (O)tetrakis(triphenylphosphine) (1.03 g, 0.89 mmol), copper (I) iodide(0.14 g, 0.74 mmol), 3-methybut-1-yn-3-ol (2.55 g, 30.4 mmol) anddi-isopropylamine (50 ml). The crude product was purified by flashchromatography [fine mesh silica gel; 10% (v/v) ethyl acetate in petrol(bp 40°-60° C.)] to give a yellow solid which was recrystallized fromcyclohexane and dried in vacuo (P₂ O₅, 0.20 mm Hg, RT, 18 hours).

Yield=2.34 g, (43%) mp=44°-45° C.

COMPOUND 15 Preparation of2-Fluoro-1-(3-hydroxy-3-methylbut-1-ynyl)-4-pentadecyloxybenzene

This compound was prepared using a similar method to that described forcompound 12. Quantities: compound 6 (4.22 g, 10.5 mmol), palladium (O)tetrakis(triphenylphosphine) (1.0 g, 0.87 mmol), copper (I) iodide (0.14g, (0.74 mmol), 3-methybut-1-yn-3-ol (1.90 g, 22.6 mmol) anddi-isopropylamine (50 ml). The crude product was purified by flashchromatography [fine mesh silica gel; 5% (v/v) ethyl acetate in petrol(bp 40°-60° C.)] to give an orange oil which crystallised on standing.This was recrystallized from cyclohexane and dried in vacuo (P₂ O₅, 0.20mm Hg, RT, 6 hours).

Yield=1.57 g, (37%) mp=40°-41° C.

COMPOUND 16 Preparation of3-Fluoro-4-dodecyloxy-1-(3-hydroxy-3-methylbut-1-ynyl)benzene

This compound was prepared using a similar method to that described forcompound 12. Quantities: compound 7 (5.00 g, 13.9 mmol), palladium (O)tetrakis(triphenylphosphine) (1.03 g, 0.89 mmol), copper (I) iodide(0.12 g, (0.63 mmol), 3-methybut-1-yn-3-ol (2.54 g, 30.2 mmol) anddi-isopropylamine (40 ml). The crude product was purified by flashchromatography [fine mesh silica gel; 1:1 dichloromethane-petrol (bp40°-60° C.)]; to give an orange solid which was recrystallized fromcyclohexane and dried in vacuo (P₂ O₅, 0.30 mm Hg, RT, 10 hours).

Yield=3.58 g, (71%) mp=30°-32° C.

COMPOUND 17 Preparation of3-Fluoro-1-(3-hydroxy-3-methylbut-1-ynyl)-4-tridecyloxybenzene

This compound was prepared using a similar method to that described forcompound 12. Quantities: compound 8 (5.20 g, 13.9 mmol), palladium (O)tetrakis(triphenylphosphine) (1.03 g, 0.89 mmol), copper (I) iodide(0.14 g, (0.74 mmol), 3-methybut-1-yn-3-ol (2.54 g, 30.2 mmol) anddi-isopropylamine (40 ml). The crude product was purified by flashchromatography [fine mesh silica gel; 10% (v/v) ethyl acetate in petrol(bp 40°-60° C.)]; to give a yellow solid which was recrystallized fromcyclohexane and dried in vacuo (P₂ O₅, 0.20 mm Hg, RT, 20 hours).

Yield=4.63 g, (88%) mp=46°-48° C.

COMPOUND 18 Preparation of3-Fluoro-1-(3-hydroxy-3-methylbut-1-ynyl)-4-tetradecyloxybenzene

This compound was prepared using a similar method to that described forcompound 12. Quantities: compound 9 (5.40 g, 13.9 mmol), palladium (O)tetrakis(triphenylphosphine) (1.05 g, 0.91 mmol), copper (I) iodide(0.13 g, (0.68 mmol), 3-methybut-1-yn-3-ol (2.54 g, 30.2 mmol) anddi-isopropylamine (40 ml). The crude product was purified by flashchromatography [fine mesh silica gel; 10% (v/v) ethyl acetate in petrol(bp 40°-60° C.)]; the white solid recrystallized from cyclohexane anddried in vacuo (P₂ O₅, 0.40 mm Hg, RT, 24 hours).

Yield=4.16 g, (76%) mp=45°-46° C.

COMPOUND 19 Preparation of3-Fluoro-1-(3-hydroxy-3-methylbut-1-ynyl)-4-pentadecyloxybenzene

This compound was prepared using a similar method to that described forcompound 12. Quantities: compound 10 (5.58 g, 13.9 mmol), palladium (O)tetrakis(triphenylphosphine) (1.02 g, 0.88 mmol), copper (I) iodide(0.11 g, (0.58 mmol), 3-methybut-1-yn-3-ol (2.54 g, 30.2 mmol) anddi-isopropylamine (50 ml). The crude product was purified by flashchromatography [fine mesh silica gel; 5% (v/v) ethyl acetate in petrol(bp 40°-60° C.)]; the yellow solid was recrystallized from cyclohexaneand dried in vacuo (P₂ O₅, 0.20 mm Hg, RT, 72 hours).

Yield=5.05 g, (90%) mp=54°-55° C.

COMPOUND 20 Preparation of3-Fluoro-4-hexadecyloxy-1-(3-hydroxy-3-methylbut-1-ynyl)benzene

This compound was prepared using a similar method to that described forcompound 12. Quantities: compound 11 (6.02 g, 14.5 mmol), palladium (O)tetrakis(triphenylphosphine) (1.01 g, 0.9 mmol), copper (I) iodide (0.17g, 0.9 mmol), 3-methybut-1-yn-3-ol (2.46 g, 29.2 mmol) anddi-isopropylamine (60 ml). The crude product was purified by flashchromatography [fine mesh silica gel; 5% (v/v) ethyl acetate in petrol(bp 40°-60° C.)]; the yellow solid obtained was recrystallized fromcyclohexane and dried in vacuo (P₂ O₅, 0.20 mm Hg, RT, 5 hours).

Yield=4.68 g, (77%) mp=49°-50° C.

COMPOUND 21 4-Dodecyloxy-1-ethynyl-2-fluorobenzene

Compound 12 (3.85 g, 10.6 mmol), potassium hydroxide (0.62 g, 11.1 mmol)and toluene (100 ml) were stirred and heated under reflux under nitrogenfor 2 hours. The acetone and toluene azeotrope was removed periodicallyvia a Dean and Stark receiver and replaced with an equal volume oftoluene. The cooled reaction mixture was poured onto water (100 ml) andthe organic phase separated. The aqueous phase was then washed withdiethyl ether (3×50 ml) and recombined with the organic layer beforebeing washed with brine (50 ml), dried (MgSO₄), filtered and evaporatedto give an orange oil. This was purified by flash chromatography [finemesh silica gel; petrol (bp 40°-60° C.)] the yellow solid obtained wasrecrystallised (cyclohexane) and dried in vacuo (P₂ O₅, 0.30 mm Hg, RT,5 hours).

Yield=2.28 g (71%) mp=35°-36° C.

Compound 21-19 have general formula V, see Table 3. ##STR10##

COMPOUND 22 1-Ethynyl-2-fluoro-4-tridecyloxybenzene

This compound was prepared using a similar method to that described forcompound 21. Quantities: compound 13 (3.08 g, 8.19 mmol) potassiumhydroxide (0.53 g, 9.45 mmol and toluene (80 ml). The crude product waspurified by flash chromatography [fine mesh silica gel; 9:1dichloromethane-petrol (bp 40°-60° C.)]; the brown solid obtained wasrecrystallized from cyclohexane and dried in vacuo (P₂ O₅, 0.10 mm Hg,40° C., 7 hours).

Yield=1.89 g, (72%) mp=40°-41° C.

COMPOUND 23 1-Ethynyl-2-fluoro-4-tetradecyloxybenzene

This compound was prepared using a similar method to that described forcompound 21. Quantities: compound 14 (2.35 g, 6.02 mmol) potassiumhydroxide (0.39 g, 6.95 mmol and toluene (70 ml). The crude product waspurified by flash chromatography [fine mesh silica gel;dichloromethane]; the yellow solid obtained was recrystallised fromcyclohexane and dried in vacuo (P₂ O₅, 0.10 mm Hg, 40° C., 3 hours).

Yield=1.28 g, (64%) mp=41°-42° C.

COMPOUND 24 1-Ethynyl-2-fluoro-4-pentadecyloxybenzene

This compound was prepared using a similar method to that described forcompound 21. Quantities: compound 15 (1.53 g, 3.8 mmol) potassiumhydroxide (0.26 g, 4.6 mmol and toluene (100 ml). The crude product waspurified by flash chromatography [fine mesh silica gel;dichloromethane]; the yellow solid obtained was recrystallised fromcyclohexane and dried in vacuo (P₂ O₅, 0.30 mm Hg, RT, 18 hours).

Yield=1.17 g, (88%) mp=41°-42° C.

COMPOUND 25 1-Ethynyl-3-fluoro-4-dodecyloxybenzene

This compound was prepared using a similar method to that described forcompound 21. Quantities: compound 16 (3.49 g, 9.64 mmol) potassiumhydroxide (0.62 g, 11.07 mmol and toluene (100 ml). The crude productwas purified by flash chromatography [fine mesh silica gel; 9:1dichloromethane-petrol (bp 40°-60° C.)]; the yellow solid obtained wasdried in vacuo (P₂ O₅, 0.40 mm Hg, RT, 6 hours).

Yield=2.65 g, (90%) mp--not recorded

COMPOUND 26 1-Ethynyl-3-fluoro-4-tridecyloxybenzene

This compound was prepared using a similar method to that described forcompound 21 Quantities: compound 17 (4.56 g, 12.2 mmol) potassiumhydroxide (0.76 g, 13.5 mmol and toluene (100 ml). The crude product waspurified by flash chromatography [fine mesh silica gel; 9:1dichloromethane-petrol (bp 40°-60° C.]; the yellow solid obtained wasdried in vacuo (P₂ O₅, 0.40 mm Hg, RT, 4 hours).

Yield=3.54 g, (91%) mp=39°-41° C.

COMPOUND 27 1-Ethynyl-3-fluoro-4-tetradecyloxybenzene

This compound was prepared using a similar method to that described forcompound 21. Quantities: compound 18 (4.06 g, 10.4 mmol) potassiumhydroxide (0.62 g, 11.1 mmol and toluene (100 ml). The crude product waspurified by flash chromatography [fine mesh silica gel; 9:1dichloromethane-petrol (bp 40°-60° C.)]; the yellow solid obtained wasdried in vacuo (P₂ O₅, 0.35 mm Hg, RT, 6 hours).

Yield=3.08 g, (89%) mp=34°-35° C.

COMPOUND 28 1-Ethynyl-3-fluoro-4-pentadecyloxybenzene

This compound was prepared using a similar method to that described forcompound 21. Quantities: compound 19 (4.99 g, 12.35 mmol) potassiumhydroxide (0.73 g, 13.01 mmol and toluene (100 ml). The crude productwas purified by flash chromatography [fine mesh silica gel; 9:1dichloromethane-petrol (bp 40°-60° C.)]; the orange solid obtained wasrecrystallised from cyclohexane and dried in vacuo (P₂ O₅, 0.20 mm Hg,40° C., 5 hours).

Yield=2.69 g, (68%) mp=45°-47° C.

COMPOUND 29 1-Ethynyl-3-fluoro-4-hexadecyloxybenzene

This compound was prepared using a similar method to that described forcompound 21. Quantities: compound 20 (4.61 g, 8.8 mmol) potassiumhydroxide (0.52 g, 9.2 mmol) and toluene (120 ml). The crude product waspurified by flash chromatography [fine mesh silica gel;dichloromethane]; the yellow solid obtained was dried in vacuo (P₂ O₅,0.30 mm Hg, RT, 18 hours).

Yield=2.89 g, (91%) mp=37°-39° C.

COMPOUND 30 3-(2-Fluoro-4-dodecyloxyphenyl)propiolic Acid

Butyllithium (2.8 ml, 2.5M in hexanes) was added dropwise to a stirred,cooled (-78° C.) solution of compound 21 (2.10 g, 6.91 mmol) in dry thf(100 ml) under nitrogen. The resulting solution was kept at -78° C. fora further 1.5 hours before being poured onto a stirred slurry of crushed`Cardice` and dry thf (100 ml) and allowed to warm to room temperatureovernight. The solution was acidified with concentrated hydrochloricacid and water (100 ml) added. The product was extracted with diethylether (3×50 ml). The combined ethereal extracts were then washed withbrine (50 ml), dried (MgSO₄), filtered and evaporated to give a yellowsolid. The product was purified by flash chromatography [fine meshsilica gel; dichloromethane (initially) and 9:1 dichloromethane-methanol(finally)]. Two fractions were obtained and recrystallised fromcyclohexane and dried in vacuo (P₂ O₅, 0.30 mm Hg, RT, 10 hours), thefirst proving to be unreacted compound 21.

Yield=0.87 g, (36%) mp--not recorded

Compounds 30-38 have general formula VI, see Table 4. ##STR11##

COMPOUND 21 3-(2-Fluoro-4-tridecyloxyphenyl)propiolic Acid

Butyllithium (2.4 ml, 2.5M in hexanes) was added dropwise to a stirred,cooled (-10° C.) solution of compound 22 (1.80 g, 5.66 mmol) in dry thf(40 ml) under nitrogen. The reaction was stirred for a further 10 min at-10° C. before being poured onto a stirred slurry of crushed `Cardice`and dry thf (20 ml) with stirring and allowed to warm to roomtemperature. The solution was acidified with concentrated hydrochloricacid and then diluted with water (100 ml). The organic phase was thenseparated and the aqueous phase washed with diethyl ether (2×50 ml). Thecombined organic phases were then washed with brine (50 ml), dried(MgSO₄), filtered and evaporated to give a brown liquid. The product waspurified by flash chromatography [fine mesh silica gel; dichloromethane(initially) and 9:1 dichloromethane-methanol (finally)]; to give a brownsolid which was recrystallised from cyclohexane and dried in vacuo (P₂O₅, 0.20 mm Hg, 40° C., 5 hours).

Yield=0.84 g, (41%) mp=98°-99° C.

COMPOUND 32 3-(2-Fluoro-4-tetradecyloxyphenyl)propiolic Acid

This compound was prepared using a similar method to that described forcompound 31. Quantities: compound 23 (1.21 g, 3.6 mmol), butyllithium(1.5 ml, 2.5M in hexanes) and dry thf (35 ml). The crude product waspurified by flash chromatography [fine mesh silica gel; dichloromethane(initially) and 9:1 dichloromethane-methanol (finally)]; to give a brownsolid which was recrystallised (ethanol) and dried in vacuo (P₂ O₅, 0.20mm Hg, 40° C., 5 hours).

Yield=0.97 g, (71%) mp=90°-109(dec)° C.

COMPOUND 33 3-(2-Fluoro-4-pentadecyloxyphenyl)propiolic Acid

This compound was prepared using a similar method to that described forcompound 31. Quantities: compound 24 (1.16 g, 3.4 mmol), butyllithium(1.4 ml, 2.5M in hexanes) and dry thf (35 ml). The crude product waspurified by flash chromatography [fine mesh silica gel; dichloromethane(initially) and 9:1 dichloromethane-methanol (finally)]; to give a darkgreen solid which was recrystallised (cyclohexane) and dried in vacuo(P₂ O₅, 0.30 mm Hg, 35° C., 5 hours).

Yield=0.77 g, (58%) mp=100°-102° C.

COMPOUND 34 3-(3-Fluoro-4-dodecyloxyphenyl)propiolic Acid

This compound was prepared using a similar method to that described forcompound 31. Quantities: compound 25 (2.48 g, 8.16 mmol), butyllithium(3.3 ml, 2.5M in hexanes) and dry thf (40 ml). The pale yellow solidobtained from flash chromatography was recrystallised (cyclohexane) anddried in vacuo (P₂ O₅, 0.10 mm Hg, 40° C., 4 hours).

Yield=1.70 g, (60%) mp=89°-93° C.

COMPOUND 35 3-(3-Fluoro-4-tridecyloxyphenyl)propiolic Acid

This compound was prepared using a similar method to that described forcompound 31. Quantities: compound 26 (1.71 g, 5.4 mmol), butyllithium(2.2 ml, 2.5M in hexanes) and dry thf (35 ml). The pale yellow solidobtained after flash chromatography was recrystallised (cyclohexane) anddried in vacuo (P₂ O₅, 0.10 mm Hg, 40° C., 18 hours).

Yield=1.12 g, (57%) mp=91°-94° C.

COMPOUND 36 3-(3-Fluoro-4-tetradecyloxyphenyl)propiolic Acid

This compound was prepared using a similar method to that described forcompound 31. Quantities: compound 27 (3.03 g, 9.1 mmol), butyllithium(3.8 ml, 2.5M in hexanes) and dry thf (35 ml). The yellow solid obtainedafter flash chromatography was recrystallised (cyclohexane-ethylacetate), washed with petrol (bp 40°-60° C.) (1 ml) and dried in vacuo(P₂ O₅, 0.10 mm Hg, 45° C., 5 hours).

Yield=2.47 g, (72%) mp=91°-93° C.

COMPOUND 37 3-(3-Fluoro-4-pentadecyloxyphenyl)propiolic Acid

This compound was prepared using a similar method to that described forcompound 31. Quantities: compound 28 (2.62 g, 7.57 mmol), butyllithium(3.2 ml, 2.5M in hexanes) and dry thf (50 ml). The yellow solid obtainedafter flash chromatography was recrystallised (cyclohexane) and dried invacuo (P₂ O₅, 0.10 mm Hg, 40° C., 5 hours).

Yield=1.67 g, (56%) mp=95°-97° C.

COMPOUND 38 3-(3-Fluoro-4-hexadecyloxyphenyl)propiolic Acid

This compound was prepared using a similar method to that described forcompound 31. Quantities: compound 29 (3.58 g, 9.9 mmol), butyllithium(4.00 ml, 2.5M in hexanes) and dry thf (50 ml). The crude product waspurified by flash chromatography [fine mesh silica gel; dichloromethane(initially) and 9:1 dichloromethane-methanol (finally)]; the yellowsolid obtained was recrystallised (cyclohexane) and dried in vacuo (P₂O₅, 0.30 mm Hg, 30° C., 5 hours).

Yield=2.53 g, (63%) mp=93°-96° C.

COMPOUND 40 4'-Hydroxybiphenyl-4-carboxylic Acid

A mixture of concentrated sulphuric acid (115 ml) and water (115 ml) wasadded dropwise to a stirred suspension of 4-cyano-4'-hydroxybiphenyl 39(25.62 g, 131.4 mmol) in glacial acetic acid (400 ml). The mixture washeated under reflux for 48 hours, the cooled reaction mixture was thenpoured into water (600 ml) with stirring and the white precipitatefiltered off. The aqueous filtrate was then washed with diethyl ether(4×70 ml); the combined extracts were then washed with water (50 ml),dried (MgSO₄) filtered and evaporated to give a white solid, both cropsof product were combined, dried thoroughly and recrystallised (glacialacetic acid) and dried in vacuo (P₂ O₅, 0.30 mm Hg, 50° C., 5 hours).

Yield=23.49 g, (84%) mp--not recorded

COMPOUND 41 4'-Methoxycarbonyloxybiphenyl-4-carboxylic Acid

Compound 40 (15.02 g, 70.2 mmol) was added slowly to a vigorouslystirred solution of sodium hydroxide (8.15 g, 203.8 mmol) in water (300ml) at -4° C. Methyl chloroformate (10.82 g, 114.5 mmol) was addeddropwise and the temperature maintained at 0° C. The resulting whiteslurry was then stirred under these conditions for a further 4 hours.The pH was then adjusted to 5 using concentrated hydrochloric acidsolution (1:1, conc HCl-water) and the voluminous white precipitatefiltered off and washed with water. The white solid was dried andrecrystallised (glacial acetic acid) and dried in vacuo (P₂ O₅, 0.20 mmHg, 40° C., 4 hours).

Yield=14.83 g, (78%) mp=256°-260° C.

COMPOUND 42 (R)-1-Methylheptyl4'-methoxycarbonyloxybiphenyl-4-carboxylate

Triphenylphosphine (6.80 g, 25.9 mmol) and (S)-octan-2-ol (5.03 g, 38.6mmol) in dry thf (25 ml) was added dropwise to a stirred mixture ofcompound 41 (7.03 g, 25.8 mmol) and diethyl azodicarboxylate (4.50 g,25.9 mmol) in dry thf (40 ml) under nitrogen. The reaction was stirredfor a further 24 hours at room temperature. The white precipitate wasremoved by filtrate through a pad of `Hyflo-supercel`, the filtrate wasthen washed with brine (50 ml), dried (MgSO₄), filtered and evaporatedto give a white solid. This was purified by flash chromatography [finemesh silica gel: 5% (v/v) ethyl acetate in petrol (bp 40°-60° C.)] togive a colourless oil which was dried in vacuo (P₂ O₅, 0.20 mm Hg, RT, 5hours).

Yield=8.06 g, (81%)

COMPOUND 43 (S)-1-Methylheptyl4'-methoxycarbonyloxybiphenyl-4-carboxylate

This compound was prepared using a similar method to that described forcompound 42. Quantities: triphenylphosphine (6.74 g, 25.7 mmol),(R)-octan-2-ol (5.03 g, 38.7 mmol), compound 41 (7.00 g, 25.7 mmol),diethyl azodicarboxylate (4.50 g, 25.9 mmol) and dry thf (110 ml). Thecrude product was purified by flash chromatography [fine mesh silicagel; 5% (v/v) ethyl acetate in petrol (bp 40°-60° C.)]; to give acolourless liquid which was dried in vacuo (P₂ O₅, 0.20 mm Hg, RT, 5hours).

Yield=7.98 g, (81%)

COMPOUND 44 (R)-1-Methylheptyl 4'-hydroxybiphenyl-4-carboxylate

A solution of compound 42 (8.06 g, 20.9 mmol) in ethanol (30 ml) wasadded dropwise to a stirred mixture of ammonia (105 ml, 35% solution)and ethanol (180 ml) at room temperature. TLC analysis showed completereaction after a period of 30 min. The reaction was then poured intowater (300 ml) and cooled in `Cardice`, the precipitated product wasthen filtered off, dried and recystallised (cyclohexane-ethyl acetate,4:1), the colourless crystals were then dried in vacuo (P₂ O₅, 0.10 mmHg, 40° C., 5 hours).

Yield=5.52 g, (81%) mp=84°-87° C.

COMPOUND 45 (S)-1-Methylheptyl 4'-hydroxybiphenyl-4-carboxylate

This compound was prepared using a similar method to that described forcompound 44. Quantities compound 43 (7.51 g, 19.6 mmol), ethanol (210ml) and ammonia (105 ml, 35% solution).

Yield=4.89 g, (77%) mp=87°-89° C.

COMPOUND 46 (R)-1-Methylheptyl4'-[(2-fluoro-4-dodecyloxyphenyl)propioloyloxy]biphenyl-4-carboxylate

Dicyclohexylcarbodiimide (0.31 g, 1.5 mmol) was added to a stirredmixture of compound 30 (0.42 g, 1.2 mmol), compound 44 (0.39 g, 1.2mmol), 4-N,N-dimethylaminopyridine (0.05 g, 0.4 mmol) in drydichloromethane (10 ml) at room temperature and then stirred for afurther 18 hours. The reaction was diluted with dichloromethane (50 ml)and the precipitate was removed by filtrate through a pad of`Hyflo-supercel` and the filtrate washed successively with water (50ml), 5% (v/v) acetic acid solution (2×50 ml), water (50 ml) before beingdried (MgSO₄), filtered and evaporated to give an orange solid. This waspurified twice by flash chromatography, first [fine mesh silica gel; 5%(v/v) ethyl acetate in petrol (bp 40°-60° C.)] and then [fine meshsilica gel; 9:1 dichloromethane-petrol (bp 40°-60° C.)] to give acolourless solid which was recrystallised (cyclohexane, twice) and driedin vacuo (P₂ O₅, 0.20 mm Hg, 50° C., 7 hours).

Yield=0.17 g, (22%)

Phase Transition Temperatures/°C. (on cooling)

    I 87.1 S.sub.A 86.8 S.sub.c ° 49.8 K

Compounds 46-53 have general formula VII, see Table 5. ##STR12##

COMPOUND 47 (S)-1-Methylheptyl4'-[(2-fluoro-4-dodecyloxyphenyl)propioloyloxy]biphenyl-4-carboxylate

This compound was prepared using a similar method to that described forcompound 46. Quantities: dicyclohexylcarbodiimide (0.31 g, 1.5 mmol),compound 30 (0.40 g, 1.2 mmol), compound 45 (0.33 g, 1.0 mmol),4-N,N-dimethylaminopyridine (0.04 g, 0.3 mmol) and dry dichloromethane(16 ml). The crude product was purified twice by flash chromatography,first [fine mesh silica gel; 5% (v/v) ethyl acetate in petrol (bp40°-60° C.)] and then [fine mesh silica gel; 9:1 dichloromethane-petrol(bp 40°-60° C.)]; to give a white solid which was recrystallised(cyclohexane, three times) and dried in vacuo (P₂ O₅, 0.30 mm Hg, 40°C., 5 hours).

Yield=0.24 g, (36%)

    I 87.1 S.sub.A 86.5 S.sub.c * 57.6 K

COMPOUND 48 (S)-1-Methylheptyl4'-[(3-fluoro-4-dodecyloxyphenyl)propioloyloxy]biphenyl-4-carboxylate

This compound was prepared using a similar method to that described forcompound 46. Quantities: dicyclohexylcarbodiimide (0.37 g, 1.8 mmol),compound 34 (0.57 g, 1.6 mmol), compound 44 (0.51 g, 1.6 mmol),4-N,N-dimethylaminopyridine (0.06 g, 0.5 mmol) and dry dichloromethane(10 ml). The crude product was purified twice by flash chromatography,first [fine mesh silica gel; 5% (v/v) ethyl acetate in petrol (bp40°-60° C.)] and then [fine mesh silica gel; 9:1 dichloromethane-petrol(bp 40°-60° C.)]; to give a colourless solid which was recrystallised(cyclohexane, twice) and dried in vacuo (P₂ O₅, 0.20 mm Hg, 40° C., 5hours).

Yield=0.31 g, (30%)

    I 75.1 S.sub.c * 74.0 K

COMPOUND 49 (S)-1-Methylheptyl4'-[(3-fluoro-4-dodecyloxyphenyl)propioloyloxy]biphenyl-4-carboxylate

This compound was prepared using a similar method to that described forcompound 46. Quantities: dicyclohexylcarbodiimide (0.37 g, 1.8 mmol),compound 34 (0.54 g, 1.6 mmol), compound 45 (0.50 g, 1.6 mmol),4-N,N-dimethylaminopyridine (0.04 g, 0.3 mmol) and dry dichloromethane(10 ml). The crude product was purified twice by flash chromatography,first [fine mesh silica gel; 5% (v/v) ethyl acetate in petrol (bp40°-60° C.)] and then [fine mesh silica gel; 9:1 dichloromethane-petrol(bp 40°-60° C.)]; to give a colourless solid which was recrystallised(cyclohexane, three times) and dried in vacuo (P₂ O₅, 0.10 mm Hg, 40°C., 72 hours).

Yield=0.47 g, (47%)

    I 75.5 S.sub.c ° 58.2 K

COMPOUND 50 (R)-1-Methylheptyl4'-[(3-fluoro-4-tridecyloxyphenyl)propioloyloxy]biphenyl-4-carboxylate

This compound was prepared using a similar method to that described forcompound 46. Quantities: dicyclohexylcarbodiimide (0.54 g, 2.62 mmol),compound 35 (0.56 g, 1.6 mmol), compound 44 (0.51 g, 1.6 mmol),4-N,N-dimethylaminopyridine (0.05 g, 0.4 mmol) and dry dichloromethane(10 ml). The crude product was purified twice by flash chromatography,first [fine mesh silica gel; 5% (v/v) ethyl acetate in petrol (bp40°-60° C.)] and then [fine mesh silica gel; 9:1 dichloromethane-petrol(bp 40°-60° C.)]; to give a colourless solid which was recrystallised(cyclohexane, twice) and dried in vacuo (P₂ O₅, 0.10 mm Hg, 50° C., 6hours).

Yield=0.16 g, (15%)

    I 74.6 S.sub.c ° 66.5 K

COMPOUND 51 (S)-1-Methylheptyl4'-[(3-fluoro-4-tridecyloxyphenyl)propioloyloxy]biphenyl-4-carboxylate

This compound was prepared using a similar method to that described forcompound 46. Quantities: dicyclohexylcarbodiimide (0.40 g, 1.9 mmol),compound 35 (0.58 g, 1.6 mmol), compound 45 (0.51 g, 1.6 mmol),4-N,N-dimethylaminopyridine (0.05 g, 0.4 mmol) and dry dichloromethane(10 ml). The crude product was purified twice by flash chromatography,first [fine mesh silica gel; 5% (v/v) ethyl acetate in petrol (bp40°-60° C.)] and then [fine mesh silica gel; 9:1 dichloromethane-petrol(bp 40°-60° C.)]; to give a colourless solid which was recrystallised(cyclohexane, twice) and dried in vacuo (P₂ O₅, 0.10 mm Hg, 40° C., 8hours).

Yield=0.13 g, (12%)

    I 74.2 S.sub.c ° 63.5 K

COMPOUND 52 (R)-1-Methylheptyl4'-[(3-fluoro-4-tetradecyloxyphenyl)propioloyloxy]biphenyl-4-carboxylate

This compound was prepared using a similar method to that described forcompound 46. Quantities: dicyclohexylcarbodiimide (0.35 g, 1.7 mmol),compound 36 (0.59 g, 1.6 mmol), compound 44 (0.50 g, 1.5 mmol),4-N,N-dimethylaminopyridine (0.04 g, 0.3 mmol) and dry dichloromethane(10 ml). The crude product was purified twice by flash chromatography,first [fine mesh silica gel; 5% (v/v) ethyl acetate in petrol (bp40°-60° C.)] and then [fine mesh silica gel; 9:1 dichloromethane-petrol(bp 40°-60° C.)]; to give a colourless solid which was recrystallised(cyclohexane, twice) and dried in vacuo (P₂ O₅, 0.10 mm Hg, 40° C., 6hours).

Yield=0.15 g, (14%)

    I 75.4 S.sub.c ° 49.6 K

COMPOUND 53 (S)-1-Methylheptyl4'-[(3-fluoro-4-tetradecyloxyphenyl)propioloyloxy]biphenyl-4-carboxylate

This compound was prepared using a similar method to that described forcompound 46. Quantities: dicyclohexylcarbodiimide (0.37 g, 1.8 mmol),compound 36 (0.58 g, 1.5 mmol), compound 45 (0.50 g, 1.5 mmol),4-N,N-dimethylaminopyridine (0.03 g, 0.25 mmol) and dry dichloromethane(10 ml). The crude product was purified twice by flash chromatography,first [fine mesh silica gel; 5% (v/v) ethyl acetate in petrol (bp40°-60° C.)] and then [fine mesh silica gel; 9:1 dichloromethane-petrol(bp 40°-60° C.)]; to give a colourless solid which was recrystallised(cyclohexane, twice) and dried in vacuo (P₂ O₅, 0.30 mm Hg, 40° C., 17hours).

Yield=0.18 g, (17%)

    I 75.5 S.sub.c ° 62.7 K

Compounds of formula I may be mixed with a wise range of hosts, forexample smectic hosts to form a useful liquid crystal composition. Suchcompositions can have a range of Ps values. Compounds of formula I maybe mixed with one or more of the types of hosts VIII-XIII. Thesedifferent types of hosts maybe mixed together to which the compound ofgeneral formula I may also be added.

Typical hosts include:

The compounds described in PCT/GB86/00040, eg of formula VIII ##STR13##where R₁ and R₂ are independently C₃ -C₁₂ alkyl or alkoxy.

The fluoro-terphenyls described in EPA 84304894.3 and GBA 8725928, eg offormula IX ##STR14## where R₁ and R₂ are independently C₃ -C₁₂ alkyl oralkoxy, x is 1 and F may be on any of the available substitutionpositions on the phenyl ring specified.

The difluoro-terphenyls described in GBA 8905422.5, eg of formula X##STR15## where R₁ and R₂ are independently C₃ -C₁₂ alkyl or alkoxy.

The phenyl-pyrimidines described in WO 86/00087, eg of formula XI##STR16## including those compounds were R₁ is C₃ -C₁₂ aklyl and R₂ isgiven by the general formula (CH₂)_(n) --CHXCH₂ CH₃, where n is 1 to 5and X is CN or Cl.

The compounds described by R. Eidenschink et. al. inCyclohexanederivative mit Getilteneten Smedtischen Phasen at the 16thFreiberg LIquid Crystal Conference, Freiberg, Germany, p8. Availablefrom E. Merck Ltd., German, eg of formula XII. ##STR17## including thosecompounds where R₁ and R₂ are independently C₁ -C₁₅ alkyl.

The difluoro-phenyl pyrimidines described at the 2nd InternationalSymposium on Ferroelectric Liquid Crystals, Goteborg, Sweden, June 1989by Reiffenrath et. al., eg of formula XIII ##STR18## including thosecompounds where R₁ and R₂ are independently C₃ -C₉ alkyl.

An example of the use of a compound of Formula I in a liquid crystalmaterial and device embodying the present invention will now bedescribed with reference to FIG. 2.

The liquid crystal device consists of two transparent plates, 1 and 2,in this case made from glass. These plates are coated on their internalface with transparent conducting electrodes 3 and 4. An alignment layeris introduced onto the internal faces of the cell so that a planarorientation of the molecules making up the liquid crystalline materialwill be approximately parallel to the glass plates 1 and 2. This is doneby coating the glass plates 1, 2 complete with conducting electrodes 3,4 with layers of film 5 and 6 of a suitable polymer, eg polyimide. Theelectrodes 3, 4 may be formed into row and column electrodes so that theintersections between each column and row form an x, y matrix ofaddressable elements or pixels. Prior to the construction of the cellthe films 5, 6 are rubbed with a soft tissue in a given direction, thrubbing directions being arranged parallel upon construction of thecell. A spacer 7 eg of polymethyl methacrylate separates the glassplates 1 and 2 to a suitable distance eg 2 microns. Liquid crystalmaterial 8 is introduced between glass plates 1, 2 by filling the spacein between them. The spacer 7 is sealed with an adhesive 9 in a vacuumusing an existing technique. Polarisers 10, 11 are arranged in front ofand behind the cell.

The device may operate in a transmissive or reflective mode. In theformer, light passing through the device, eg from a tungsten bulb, isselectively transmitted or blocked to form the desired display. In thereflective move a mirror (12) is placed behind the second polariser 11to reflect ambient light back through the cell and two polarisers. Bymaking the mirror partly reflecting the device may be operated both in atransmissive and reflective mode.

Tables 8-11 give values for the spontaneous polarisation (Pa/nC/cm²)over a range of temperatures (°C.) for a number of the compoundsdescribed by general formula I. The compounds of formula I may be addedto host materials. Table 12 gives values of the spontaneous polarisation(Ps/nC/cm²) over a range of temperatures (°C.) when it is mixed 10% byweight with host material H1. H1 is a 1:1:1 mixture of the following:

R₁ =C₈ H₁₇, R₂ =C₅ H₁₁

R₁ =OC₈ H₁₇, R₂ =C₅ H₁₁

R₁ =OC₈ H₁₇, R₂ =C₇ H₁₅ ##STR19##

The host is a commercially available host and is widely used inferroelectric liquid crystal mixtures.

The Ps was measured in a 6 μm polyimide (PI) parallel cell using adiamant bridge and applying a sine wave at 30 Hz.

The optical tilt angle measurements detailed in FIGS. 13 and 14 show thedependence of the optical tilt angle of the S_(c) * phase with reducedtemperature and the studies were performed in 3.6 μm thick polyimidecoated cells.

FIGS. 3-12 are phase diagrams for compounds 48/49; 50/51; 52/53; 60/61;64/65; 46/47; 54/55; 56/57; 58/59; 62/63.

                  TABLE 1                                                         ______________________________________                                        Compound   R              X     Y                                             ______________________________________                                         3         C.sub.12 H.sub.25                                                                            H     F                                              4         C.sub.13 H.sub.27                                                                            H     F                                              5         C.sub.14 H.sub.29                                                                            H     F                                              6         C.sub.15 H.sub.31                                                                            H     F                                              7         C.sub.12 H.sub.25                                                                            F     H                                              8         C.sub.13 H.sub.27                                                                            F     H                                              9         C.sub.14 H.sub.29                                                                            F     H                                             10         C.sub.15 H.sub.31                                                                            F     H                                             11         C.sub.16 H.sub.33                                                                            F     H                                             ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Compound   R              X     Y                                             ______________________________________                                        12         C.sub.12 H.sub.25                                                                            H     F                                             13         C.sub.13 H.sub.27                                                                            H     F                                             14         C.sub.14 H.sub.29                                                                            H     F                                             15         C.sub.15 H.sub.31                                                                            H     F                                             16         C.sub.12 H.sub.25                                                                            F     H                                             17         C.sub.13 H.sub.27                                                                            F     H                                             18         C.sub.14 H.sub.29                                                                            F     H                                             19         C.sub.15 H.sub.31                                                                            F     H                                             20         C.sub.16 H.sub.33                                                                            F     H                                             ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Compound   R              X     Y                                             ______________________________________                                        21         C.sub.12 H.sub.25                                                                            H     F                                             22         C.sub.13 H.sub.27                                                                            H     F                                             23         C.sub.14 H.sub.29                                                                            H     F                                             24         C.sub.15 H.sub.31                                                                            H     F                                             25         C.sub.12 H.sub.25                                                                            F     H                                             26         C.sub.13 H.sub.27                                                                            F     H                                             27         C.sub.14 H.sub.29                                                                            F     H                                             28         C.sub.15 H.sub.31                                                                            F     H                                             29         C.sub.16 H.sub.33                                                                            F     H                                             ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        Compound   R              X     Y                                             ______________________________________                                        30         C.sub.12 H.sub.25                                                                            H     F                                             31         C.sub.13 H.sub.27                                                                            H     F                                             32         C.sub.14 H.sub.29                                                                            H     F                                             33         C.sub.15 H.sub.31                                                                            H     F                                             34         C.sub.12 H.sub.25                                                                            F     H                                             35         C.sub.13 H.sub.27                                                                            F     H                                             36         C.sub.14 H.sub.29                                                                            F     H                                             37         C.sub.15 H.sub.31                                                                            F     H                                             38         C.sub.16 H.sub.33                                                                            F     H                                             ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                        Compound   R              X     Y                                             ______________________________________                                        46 (R)*    C.sub.12 H.sub.25                                                                            H     F                                             47 (S)     C.sub.12 H.sub.25                                                                            H     F                                             48 (R)     C.sub.12 H.sub.25                                                                            F     H                                             49 (S)     C.sub.12 H.sub.25                                                                            F     H                                             50 (R)     C.sub.13 H.sub.27                                                                            F     H                                             51 (S)     C.sub.13 H.sub.27                                                                            F     H                                             52 (R)     C.sub.14 H.sub.29                                                                            F     H                                             53 (S)     C.sub.14 H.sub.29                                                                            F     H                                             ______________________________________                                         *optical isomer                                                          

In a manner similar to that for compounds 46-54, compounds 54-65 werealso synthesised. Compounds 54-65 have the same general formula as thosecompounds in Table 5 and are presented in Table 6.

                  TABLE 6                                                         ______________________________________                                        Compound   R              X     Y                                             ______________________________________                                        54 (R)*    C.sub.13 H.sub.27                                                                            H     F                                             55 (S)     C.sub.13 H.sub.27                                                                            H     F                                             56 (R)     C.sub.14 H.sub.29                                                                            H     F                                             57 (S)     C.sub.14 H.sub.29                                                                            H     F                                             58 (R)     C.sub.15 H.sub.31                                                                            H     F                                             59 (S)     C.sub.15 H.sub.31                                                                            H     F                                             60 (R)     C.sub.15 H.sub.31                                                                            F     H                                             61 (S)     C.sub.15 H.sub.31                                                                            F     H                                             62 (R)     C.sub.16 H.sub.33                                                                            H     F                                             63 (S)     C.sub.16 H.sub.33                                                                            H     F                                             64 (R)     C.sub.16 H.sub.33                                                                            F     H                                             65 (S)     C.sub.16 H.sub.33                                                                            F     H                                             ______________________________________                                         *optical isomer                                                          

The phase transition data for these compounds is presented in Table 7and is as follows:

                  TABLE 7                                                         ______________________________________                                        Compound       Phase Transitions/°C.                                   ______________________________________                                        54:            I 88.4 TGB.sub.A 87.3 S.sub.A 73.4 S.sub.c °            55:            I 88.8 TGB.sub.A 88.0 S.sub.A 72.0 S.sub.c °            56:            I 85.8 TGB.sub.A 80.8 S.sub.A 72.6 S.sub.c °            57:            I 87.1 TGB.sub.A 82.9 S.sub.A 73.5 S.sub.c °            58:            I 87.7 TGB.sub.A 79.9 S.sub.c °                         59:            I 86.2 TGB.sub.A 78.3 S.sub.c °                         60:            I 76.6 S.sub.c °                                        61:            I 76.9 S.sub.c °                                        62:            I 85.4 TGB.sub.A 78.4 S.sub.c °                         63:            I 86.1 TGB.sub.A 79.4 S.sub.c °                         64:            I 77.3 S.sub.c °                                        65:            I 78.0 S.sub.c °                                        ______________________________________                                         TGB.sub.A = Twisted grain boundary A phase.                              

                  TABLE 8                                                         ______________________________________                                        Temp/°C.                                                                             Ps/nC/cm.sup.2                                                  ______________________________________                                        74            23.6                                                            72            40.5                                                            70            47.6                                                            65            63.0                                                            60            68.7                                                            55            74.8                                                            50            79.0                                                            45            77.5                                                            40            66.5                                                            ______________________________________                                         Compound 56: 5.9 μm PI parallel cell.                                 

                  TABLE 9                                                         ______________________________________                                        Temp/°C.                                                                             Ps/nC/cm.sup.2                                                  ______________________________________                                        75            42.2                                                            70            59.0                                                            65            67.7                                                            60            73.5                                                            55            73.0                                                            50            69.0                                                            ______________________________________                                         Compound 58: 6.0 μm PI parallel cell.                                 

                  TABLE 10                                                        ______________________________________                                        Temp/°C.                                                                             Ps/nC/cm.sup.2                                                  ______________________________________                                        76            50.5                                                            74            60.0                                                            72            66.0                                                            70            71.0                                                            65            81.0                                                            60            87.0                                                            ______________________________________                                         Compound 62: 6.1 μm PI parallel cell.                                 

                  TABLE 11                                                        ______________________________________                                        Temp/°C.                                                                             Ps/nC/cm.sup.2                                                  ______________________________________                                        73            69.4                                                            72            73.1                                                            70            79.1                                                            65            90.0                                                            63            93.2                                                            60            98.1                                                            55            102.5                                                           53            104.3                                                           50            106.0                                                           45            105.0                                                           43            100.4                                                           40            99.6                                                            ______________________________________                                         Compound 64: 5.5 μm PI parallel cell.                                 

                  TABLE 12                                                        ______________________________________                                        Temp/°C.                                                                             Ps/nC/cm.sup.2                                                  ______________________________________                                        81            0.3                                                             80            0.5                                                             75            --                                                              72            1.1                                                             70            1.3                                                             60            1.6                                                             50            1.5                                                             40            1.3                                                             ______________________________________                                         Compound 64 10% by weight in H1: 5.1 μm PI parallel cell.             

We claim:
 1. A compound having formula I ##STR20## where A₁ is selectedfrom alkyl, alkoxy or alkenyl and contains 3-20 carbon atoms, X₁, X₂, X₃and X₄ are independently selected from the halogen group; m, n, p and qare independently 0, 1, 2, 3 or 4 such that m+n+p+q≠0; Y is selectedfrom O and COO; A₂ is an end group of formula II ##STR21## where Z isselected from halogen, CH₃, CN, CF₃, CHF₂ ; R is a linear or branchedalkyl group containing 2-15 carbon atoms or H; R₁ is a linear orbranched alkyl group containing 1-5 carbon atoms or H.
 2. A compoundaccording to claim 1 wherein A₁ contains 6-16 carbon atoms; R contains3-10 atoms; Z is CH₃ or CN; R₁ is H; X is F and each of m, n, p and/or qis independently 0, 1 or 2 such that m+n+p+q=1 or
 2. 3. A compoundaccording to claim 1 wherein A₁ contains 9-15 carbon atoms; R contains5-7 atoms; Z is CH₃ or CN; R₁ is H; X is F and each of m, n, p and/or qis independently 0, 1 or 2 such that m+n+p+q=1 or
 2. 4. A liquid crystaldevice comprising a layer of liquid crystal material contained betweentwo spaced cell walls each bearing electrode structures and surfacetreated on facing surfaces to align liquid structures and surfacetreated on facing surfaces to align liquid crystal material molecules,characterised in that the liquid crystal material includes the compoundas described in claim
 1. 5. A liquid crystal mixture containing any ofthe compounds of claim 1 and a host material of the following generalformula ##STR22## where R₁ and R₂ are independently C₃ -C₁₂ alkyl oralkoxy.
 6. A liquid crystal mixture containing any of the compounds ofclaim 1 and a host material of the following general formula ##STR23##where R₁ and R₂ are independently C₃ -C₁₂ alkyl or alkoxy, x is 1 and Fis on any one of the available substitution positions on the phenyl ringspecified.
 7. A liquid crystal mixture containing any of the compoundsof claim 1 and a host material of the following general formula##STR24## where R₁ and R₂ are independently C₃ -C₁₂ alkyl or alkoxy. 8.A liquid crystal mixture containing any of the compounds of claim 1 anda host material of the following general formula ##STR25## where R₁ isC₃ -C₁₂ alkyl and R₂ is given by the general formula (CH₂)_(n) --CHXCH₂CH₃, where n is 1 to 5 and X is CN or Cl.
 9. A liquid crystal mixturecontaining any of the compounds of claim 1 and a host material of thefollowing general formula ##STR26## where R₁ and R₂ are independently C₁-C₁₅ alkyl or alkoxy.
 10. A liquid crystal mixture containing any of thecompounds of claim 1 and a host material of the following generalformula ##STR27## where R₁ and R₂ are independently C₃ -C₉ alkyl oralkoxy.
 11. A liquid crystal device comprising the liquid crystalmixture as in any one of claims 5-10.